Device-to-device (Device-to-Device, “D2D” for short) communication refers to direct communication performed between two devices. A device-to-device proximity service (Device to Device Proximity Service, “D2D ProSe” for short) has become a research subject in a Long Term Evolution (Long Term Evolution, “LTE” for short) Rel.12 system of the 3rd Generation Partnership Project (3rd Generation Partnership Project, “3GPP” for short), and D2D communication is supported in systems starting from the Rel.12 system.
In a conventional solution design, a user equipment (User Equipment, “UE” for short) receives various signals, such as a control signal or a data signal, that are sent only by a base station. Therefore, the user equipment determines, according to a reference signal sent by the base station, a time for detecting a signal. However, in D2D communication, factors such as a distance between user equipments need to be considered. If the user equipment detects the D2D signal only according to the time determined by using the reference signal sent by the base station, the detection may fail.